Various cutting or grinding oils are generally used in metal working processes for the purpose of lengthening the life of working tools, such as drills, millings, tools, and grinders, improving the roughness of the finished surface of a work, and improving working efficiency thereby, resulting in the increasing the productivity of machining.
Cutting or grinding oils are roughly classified into water-soluble ones which are put in use after diluting the surface-active agent and lubricant component contained therein with water, and water-insoluble ones which contain a mineral oil as a main component and are used as it is, i.e., in the form of a stock solution. In conventional cutting and grinding operations, relatively large amounts of cutting or grinding oil are supplied to a spot of the metal piece to be worked.
The most basic and important functions of cutting oils and grinding oils are lubricating and cooling properties. Generally speaking, water-insoluble cutting and grinding oils are superior in lubricating properties, while water-soluble ones are superior in cooling properties. Since the cooling properties of the water-insoluble cutting and grinding oils are inferior to that of the water-soluble ones, it is necessary to supply large amounts, ranging from several liters to over ten liters of the water-insoluble cutting or grinding oil.
Cutting oils and grinding oils which are effective for improving working efficiency have undesirable aspects, when viewing from the different side. The typical examples of such aspects are problems concerning with the environment. Regardless of whether an oil is water-soluble or water-insoluble, it is gradually deteriorated during the use thereof and finally becomes incapable of further use. For instance, a water-soluble oil is unable to be used when it undergoes the separation of the components or deteriorates the environment in terms of sanitary, caused by deteriorated stability due to the growth of microorganisms. A water-insoluble oil becomes incapable when the acid components generated with the progress of oxidation make the metal piece corrode, or the viscosity is significantly changed. Furthermore, the oil is spent by adhering to metal chips or swarf and becomes wastes.
In such a case, the deteriorated oil is disposed and then replaced with a fresh oil. The oil disposed as wastes is necessarily subjected to various treatments so as not to adversely affect the environment. For instance, cutting or grinding oils which are developed, giving an improvement in working efficiency priority, contain a large amount of chlorine-containing components which may generate dioxin upon incineration. Therefore, the removal of such components is required. For the reason of this, there have been developed cutting or grinding oils which are free of chlorine-containing components. However, even though the oils contain no chlorine-based components, there arise environmental problems, resulting from disposal of large quantities of wastes. The water-soluble oils may pollute the surrounding water area, and are therefore necessarily subjected to highly-developed treatments at increased costs.
In order to deal with the foregoing problems, it has been studied to cool a metal piece by blowing a cold air instead of using cutting or grinding oils. In such a case, the other ability of cutting and grinding oils, i.e., lubricity can not be obtained.
In order to overcome such a problem, there has been developed a system in which an oil in a minimal quantity, which is within the range of about 1/100,000 to 1/1,000,000 of the normal quantity, is supplied to a cutting or grinding spot of a work, together with a compressed fluid, such as compressed air. This system can obtain a cooling effect with compressed air and can reduce the amount of wastes due to the use of a minimal quantity of oil, resulting in the reduction of the influences on the environment, accompanied with large amounts of waste disposal. However, there has not been proposed a cutting or grinding oil having the properties required for cutting or grinding using the minimal quantity lubrication system, more specifically a cutting or grinding oil having high performances which make it possible to provide a worked product with a smooth surface, even though by the use thereof in a minimal quantity, reduce the wear of tools, and perform cutting and grinding efficiently. The development of such a cutting or grinding oil has been demanded. In the minimal quantity lubrication system, the oil is supplied in the form of mist. Therefore, the system involves a problem that the oil easily adheres to the interior of a working machine, a workpiece, the inside of a mist collector and the like. If the adhered oil becomes sticky easily, the treatability thereof is hindered, leading to reduced working efficiency. Therefore, the oils for the minimal quantity lubrication system is desirously hard to be sticky.